Acidity Enhanced Pillared Clay Catalysts. Modification of Exchangeable Sites on Fluor-tetrasilicic Mica by the Fixed Interlayer Cations

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Abstract
By the use of fluor-tetrasilicic mica (TSM) as a starting material, La3+-modified pillared TSM was prepared by calcining La3+-exchanged TSM followed by Al-pillaring. Nonmodified pillared TSM managed only a 0.1% conversion for toluene alkylation with methanol, but the alkylation activity was greatly enhanced by the modification to give more than a 7% conversion, the activity level of which was roughly comparable to that of the conventional pillared montmorillonite. The effect of modification greatly depended on the calcination temperature at the pretreatment of La3+-exchanged TSM prior to a pillaring operation; the optimum calcination temperature was between 300 and 400 °C. Other multivalent cations with large ionic radii, such as Ce3+, Ca2+, and Sr2+, were also useful as modifiers. On the basis of the results of measurements involving X-ray diffraction, cation-exchange capacity and IR spectra of the adsorbed pyridine, it was concluded that a part of the thermally dehydrated La3+ ions lost their exchangeability to be fixed on the cation exchange sites of layers, remained between layers even after Al-pillaring, and took charge of the genesis of acidic sites.